Compatibility: Fits many standard CO2 cylinders with the conventional trapezoidal thread TR21-4. Allows you to use CO2 cylinders from previous versions with water aerators DUO, Art, and Terra. High-Quality Material: Made from premium brass, our CO2 adapter is rust-resistant, wear-resistant, and high-strength, ensuring enhanced safety and a long service life. Easy to Install: Connect one end of the quick adapter to the Duo water carbonator and the other end (TR21-4) to the 60-liter CO2 bottle. For DUO and ART machines of the new version, a small portion of the bottle compartment shell may need to be trimmed to insert the bottle. Efficient and Economical: Continue using your original CO2 cylinders, saving the hassle and cost of exchanging them. This adapter allows you to utilize CO2 cylinders from previous versions. Important Note: Before purchasing, ensure your CO2 cylinder, including the valve, is original (not Quooker). Otherwise, the Quick CO2 adapter may not screw in far enough to function correctly in the new soda machine. Color: Red Material: Metal Package Contents: 1 x CO2 Quick Adapter 1 x Sealing Ring (Note: Other products are not included. Light reflection and different displays may cause slight color variations.)